Inhibitors of Trichoderma reesei β-glucosidase activity derived from autohydrolysis-exploded Eucalyptus regnans

Summary

Enzymic saccharification of Eucalyptus regnans pulps pretreated by autohydrolysis-steam explosion resulted in low cellulose conversions into glucose when using trichodermal cellulase preparations. The reduced levels of glucose were attributable to the production of compounds during enzymic hydrolysis which were inhibitory to β-d-glucosidase of Trichoderma reesei C-30 and in Meicelase, but not to the cellulases. Aspergillus niger β-glucosidase was not inhibited, nor were β-d-xylosidase(s) and 1,4-β-d-xylanase(s). The inhibitory compound(s) could be extracted from the enzymic hydrolyzates with ethyl acetate. The ethyl acetate extractives inhibited β-glucosidase in a competitive manner, and inhibitory action was not affected by pH. Addition of the inhibitory compound(s) to trichodermal cellulase digests of cellulose resulted in reduced glucose yields compared to a control. The inhibitory effects could be overcome when cellulase digests were supplemented with A. niger β-glucosidase resulting in higher cellulose-to-glucose conversions. The inhibitory compound(s) were localized mainly in the heartwood of E. regnans. An inhibitor compound of this type has not hitherto been reported. The presence of inhibitory compound(s) in the autohydrolysis liquor fraction is also reported.